Fix timing issue in SimpleTenantUsageSample test

If POST query, which is made in test setUp(), for some reason
takes more that 1 second to proceed (e. g. high LA value), the
test will fail due to mismatch between the expected and actual
instance uptime values.

The error is quite rare, but nevertheless happens time to time
when Jenkins runs gate jobs.

Fixes bug 1206526

Change-Id: I0418ee3f852db6dd3c5ed905490be2e48c8fd0ba
Merge "Fix timing issue in SimpleTenantUsageSample test"